Ball valves have been commonly used for years and have employed stopper members of generally spherical shape. These members are rotated about one of its axes to align or disalign its through-port with the flow passages of the body member to establish the open and closed positions of the stopper. The provision of the stopper in spherical form has a number of obvious and distinct inherent advantages, not the least of which is overall compactness of the valve and that it requires only one quarter turn of the spherical stopper to move from open to close and from close to open, as distinguished from the gate type valve where the stopper member must be shifted axially to and from closed position. As distinguished from the tapered or conical type of stopper, all difficulties of the "wedging" effect are avoided.
Ball valves generally provide for a single seal between the ball and the seat. See for example, U.S. Pat. No. 3,504,885 to Hulsey and U.S. Pat. No. 3,339,886 to Grove. In addition, secondary seals are known in the art. See U.S. Pat. No. 4,377,273. The problem of maintaining an effective seal in high pressure ball valves has long been recognized. Present designs of sealing assemblies generally provide for a single seal between the ball and the seat and some designs provide an auxiliary system for injecting a flowable sealant to the sealing areas in order to close off leaks which frequently develop between the regular sealing surfaces of the seats and closure members. Also, some designs provide the use of pressure enhanced sealing means. Prior efforts to solve the problem of maintaining a satisfactory seal in ball valves are shown in Hulsey U.S. Pat. No. 3,504,885 and Grove U.S. Pat. No. 3,339,886 referenced above. In Hulsey U.S. Pat. No. 3,504,885, two seals are shown on each side of the valve and both seals are pressure enhanced; however, only one of the seals acts to seal fluid flow in the direction of fluid flow. When one of the seals is pressure enhanced by fluid flow in one direction, the other is pressure relieving by the same fluid flow. In Grove U.S. Pat. No. 3,339,886, FIG. 9 shows a ball valve with one pressure enhanced seal which is effective only on the downstream side. In Grove U.S. Pat. No. 3,339,886, when fluid flow is reversed, the one seal is pressure relieving.
It is an objective of the invention to provide a long-lived multiple seal valve which is capable of effectively controlling fluid flow regardless of pressures and regardless of the nature of the fluid being controlled--a valve that is one in which the integrity of the seals can be tested in the line, and one that relieves excess fluid pressure.